EP patent application 89309088.6 (Vaisala Oy) Laid-Open Publication No. EP 0358507, describes a measurement system for the scattering of light, in which system the active surface of the transmitter and the receiver is formed into a single surface by means of, e.g., combined optical fiber bundles.
FR patent application 2,594,535 also discloses an embodiment similar to that described above.
Despite the significant benefits achieved by using a common active surface for both the transmitting and receiving systems via a single optical system, unexpected problems have been encountered. As the transmitted pulse has an extremely high peak intensity, the optical fibers of the transmitting system permit stray coupling to the adjacent fibers of the receiving system, whereby the receiver input amplifier is temporarily overloaded. This can cause problems particularly in near-range scattering measurement, since the receiver input amplifier is nonresponsive during the very time the near-range reflected information should typically be detected by the receiver.
The same problem is also encountered in the conventional embodiments based on a beam splitter that have the further drawback of a partial loss of transmit power in the beam-splitting optical system.